The long term goal of my research program is to determine how muscle fibers are used during locomotion. This will involve integrating information from cellular studies and whole animal studies. This approach is unusual and important because scientists generally work either on cells or whole animals but not on both. I am convinced that the functional significance of changes in maximum speed of shortening (Vmax) of muscle fiber types cannot be fully understood without integrating this cellular and wholeanimal information. Further, I believe that elucidation of the principles of how a healthy motor system works may be useful in both diagnosing diseases of the motor system and designing computer systems for aiding movement in the handicapped. The basic objective of this proposal is to compare the velocity of shortening of muscle fibers during locomotion (V) to in vitro measurements of the maximum speed of shortening that fibers are capable of shortening (Vmax). The parameter V/Vmax is extremely important in determining the power production and efficiency of muscle fibers, but heretofore unmeasured. Three animals (fish, frogs, and cats) have been chosen because they provide the best models for addressing this question. For each of the animals, the V of the muscle fibers during location will be measured by a combination of high-speed motion picture and anatomical anaysis. In each, the Vmax of different muscle fiber types will be determined by single muscle fiber mechanics techniques and where necessary, different fiber types will be determined by a combination of electrophoretic and histochemical techniques. Finally, the activity of different muscle fiber types will be determined so that V/Vmax of different fiber types can be calculated. In addition, I will determine where on the sarcomere length- tension curve fiber are operating during locomotion. I will also measure Vmax of mouse and horse fibers to determine how this parameter is adapted to different functional constraints required with size differences.